1. Field of the Invention
The present invention relates to a thermally assisted magnetic head for writing of signals by thermally assisted magnetic recording and to a head gimbal assembly (HGA) with this thermally assisted magnetic head, and a hard disk drive with this HGA.
2. Related Background Art
As the recording density of the hard disk drive increases, further improvement is demanded in the performance of the thin film magnetic head. The thin film magnetic head commonly used is a composite type thin film magnetic head of a structure in which a magnetic detecting element such as a magneto-resistive (MR) effect element and a magnetic recording element such as an electromagnetic coil element are stacked, and these elements are used to read and write data signals from and into a magnetic disk as a magnetic recording medium.
In general, the magnetic recording medium is a kind of a discontinuous body of fine magnetic particles aggregated, and each of the fine magnetic particles is made in a single magnetic domain structure. A recording bit is composed of a plurality of fine magnetic particles. Therefore, in order to increase the recording density, it is necessary to decrease the size of the fine magnetic particles and thereby decrease unevenness at borders of recording bits. However, the decrease in the size of the fine magnetic particles raises the problem of degradation of thermostability of magnetization due to decrease of volume.
A measure of the thermostability of magnetization is given by KUV/kBT. In this case, KU represents the magnetic anisotropy energy of the fine magnetic particles, V the volume of one magnetic particle, kB the Boltzmann constant, and T absolute temperature. The decrease in the size of fine magnetic particles is nothing but decrease in V, and, without any countermeasures, the decrease in V will lead to decrease of KUV/kBT and degradation of the thermostability. A conceivable countermeasure to this problem is to increase KU at the same time, but this increase of KU will lead to increase in the coercive force of the recording medium. In contrast to it, the intensity of the writing magnetic field by the magnetic head is virtually determined by the saturation magnetic flux density of a soft magnetic material making the magnetic poles in the head. Therefore, the writing becomes infeasible if the coercive force exceeds a tolerance determined from this limit of writing magnetic field intensity.
As a method of solving this problem of thermostability of magnetization there is the following proposal of so-called thermally assisted magnetic recording: while a magnetic material with large KU is used, heat is applied to the recording medium immediately before application of the writing magnetic field, to decrease the coercive force, and writing is performed in that state. This recording is generally classified under magnetic dominant recording and optical dominant recording. In the magnetic dominant recording, the dominant of writing is an electromagnetic coil element and the radiation diameter of light is larger than the track width (recording width). On the other hand, in the optical dominant recording, the dominant of writing is a light radiating portion and the radiation diameter of light is approximately equal to the track width (recording width). Namely, the magnetic field determines the spatial resolution in the magnetic dominant recording, whereas the light determines the spatial resolution in the optical dominant recording.
As examples of such thermally-assisted magnetic head recording apparatus, Patent Documents (Japanese Patent Application Laid-Open No. 2001-255254, Japanese Patent Application Laid-Open No. 2003-114184) and Non-patent Document (T. Matsumoto et al., Near-Field Optical Probe with A Beaked Metallic Plate for Thermally Assisted Magnetic Recording, pp. 6-7, MORIS2006 WORKSHOP Technical Digest, Jun. 6-8, 2003) disclose the thermally-assisted magnetic heads in which an electroconductive near-field light generator of a plate shape is disposed on a medium-facing surface and in which light is guided onto the near-field light generator from the opposite side to the medium side to generate near-field light. A pointed cusp portion is formed at an end of the near-field light generator and the near-field light is emitted mainly from this cusp portion.